Cross coil meter

ABSTRACT

Disclosed herein is a cross coil having a first coil winding for generating a first magnetic field when an electrical current flows therethrough and a second coil winding for generating a second magnetic field when an electrical current flows therethrough, and the second coil winding being wound so as to cross the first coil winding to each other. The cross coil comprises a mechanism for equalizing the magnitude of each of the first and second magnetic fields generated when identical electrical currents flows through each of the coil windings. 
     The equalizing mechanism comprises the arrangement of the turns of the windings in which the individual turns are alternately wound on top of the turns for the other winding.

This is a continuation of co-pending application Ser. No. 07/377,059filed on Jul. 10, 1989, now U.S. Pat. No. 5,061,891.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cross coil used in a cross coil-typeindicator, in particular, relates to an improved cross coil used in across coil-type indicator in which a magnetic rotor, to which a shaft ofan indicating pointer is secured, is rotated by a magnetic fieldcomponent of the cross coil.

1. Description of the Prior Art

Conventionally, an indicator shown in FIG. 1 is commonly known as thistype of cross coil type indicator. In this indicator, a disk-shapedmagnetic rotor 2 to which a shaft of an indicating pointer 1 is secured,is positioned in a rotatable manner in a coil bobbin 3 which can beseparated into an upper and a lower section. On the outer periphery ofthe coil bobbin 3 there is wound a first coil windings 4 into which isinserted a bearing 3a of the coil bobbin 3 through which the shaft ofthe indicating pointer is passed. Next a second coil windings 5, intowhich is also inserted the bearing 3a of the coil bobbin 3, is wound onthe outer periphery of the first coil 4 windings at about 90° to thefirst coil windings 4. In addition, a scale 6 is installed on a bracket3b of the coil bobbin 3 and an indicating pointer 7 is mounted to theshaft 1 on the top surface of the scale 6.

Specifically, as diagramatically illustrated in FIG. 2, in the crosscoil as described above the rotatable magnetic rotor 2 which comprises apermanent magnet is disposed in a magnetic field generated by the firstand second coil windings 4, 5.

In this configuration, the magnetic field φ₁, φ₂ produced by the firstand second coil windings 4, 5 are proportional to the product of thecurrent flowing in the first and second coil windings 4, 5 and thenumber of turns in the windings. Therefore, if the number of turns forboth the first and second coil windings 4, 5 is N and the currentsflowing in the coil windings are I_(o) sin θ and I^(o) cos θrespectively, then the magnetic field component φ is in the direction ofthe vector component of the magnetic fields φ₁, φ₂ produced by the firstand second coil windings 4, 5, and the magnetic field component is todescribe a circle corresponding to a change of the angle θ. Accordingly,by setting the angle θ to the specified measured amount each of themagnetic fields φ₁, φ₂ becomes

    φ.sub.1 =I.sub.0 sin θ·N                (1)

    φ.sub.2 =I.sub.o cos θ·N                (2),

respectively. The magnetic field component φ acts in the direction ofthe vector component of the magnetic fields φ₁ and φ₂, and its magnitudebecomes ##EQU1## and by varying the angle θ to correspond to thespecified measured amount as in FIG. 3, the direction of the magneticfield component φ corresponds to the specified measured amount.Accordingly the magnetic rotor 2 rotates in the direction of thecomponent of the magnetic field, and as a result, by rotating incooperation with an indicating pointer 7, the angle of rotation of thepointer 7 indicates the specified measured amount, which can be realizedby a driver.

However, actually, in this type of conventional cross coil, as indicatedin FIG. 4, first, the specified number of turns of the first coil 4 arewound, then, the specified number of turns of the second coil 5 arewound on the outside of the first coil 4 crossing those windings at 90°.

Therefore, in this type of conventional cross coil, as in FIG. 4,because the outer diameter of the first coil 4 which is wound on theinside differs from that of the second coil 5 which is wound on theoutside with the same number of turns, the total length of the secondcoil 5 is the longer of the two. Accordingly, when the resistance perunit length of each coil is the same, the resistance of the second coil5 is large in comparison with that of the first coil 4. Also, if thewinding is performed so that the resistances of both coils are the same,the number of turns in the outside second coil 5 would be less incomparison with the number of turns in the first coil 4.

On the other hand, the magnitude of the magnetic fields φ₁ and φ₂ of thecoils are proportional to the product of the current flowing in the coiland the number of turns of the winding, as described in equations (1)and (2). Accordingly, it is difficult for the conventional cross coil toequalize the maximum magnetic fields I_(o) ·N of the coils 4 and 5 whichare produced to correspond to the specified measured amount (the angleθ). Specifically, when identical voltages are applied to the coil 4, 5,the currents flowing in each of the coils 4, 5 are different from eachother so that the magnetic fields φ₁ and φ₂ are not identical.

For example, when the number of winding turns N is the same for eachcoil, the resistance of the outside second coil 5 is large, as outlinedabove, so that the currents I_(o) in equations (1) and (2) are not thesame, and the current in the first coil 4 becomes large in comparisonwith the second coil 5. If the currents in each coil are I₁ and I₂respectively, the magnetic fields φ₁ and φ₂ become:

    φ.sub.1 =I.sub.1 sin θ·N                (4)

    φ.sub.2 =I.sub.2 cos θ·N                (5)

and I₁ >I₂ Therefore, the magnitude of the magnetic field component θbecomes ##EQU2## and has only elliptic characteristics corresponding tothe angle θ as shown in FIG. 5.

In this type of cross coil, for example, in the case of the currentflowing for the angle θ of 45° corresponding to the specified measuredvalue, the magnetic fields φ₁ and φ₂ for the coils 4, 5, become, fromequations (4) and (5): ##EQU3## The angle for this magnetic fieldcomponent becomes ##EQU4## and does not agree with the angle (45°) whichcorresponds to the specified measured value which should be indicated.Accordingly, in a conventional cross coil, because the direction of themagnetic field component of the cross oil does not agree with thedirection of the angle θ which corresponds to the specified measuredvalue, the problem arises that the specified measured value cannot beaccurately displayed.

SUMMARY OF THE INVENTION

In view of the above problems of such conventional devices as describedabove, an object of the present invention is to provide a cross coil inwhich the magnitude of the magnetic field produced in each coil becomesidentical when identical voltages are applied to the cross coils.

Another object of the present invention is to provide a cross coil inwhich the winding process for the cross coil winding is simple, andaccurate indication characteristics are obtained when it is included inan indicator.

Still another object of the present invention is to provide a cross coilin which the winding process for the cross coil winding isunnecessitated, the cross coil is easily assembled when included in anindicator, and the cross coil can be miniaturized.

In order to achieve these objects, a cross coil according to the presentinvention comprises a pair of coils which are positioned so that theycross one another, with the individual turns alternately wound on top ofthe turns for the other coil, and the number of turns for each coil isthe same.

In the cross coil of the present invention with the above structure,since the individual turns are alternately wound on top of the turns forthe other coil, and the number of turns for each coil is the same, thetotal lengths of each coil become identical, and, accordingly, theresistances for each coil become also identical. Therefore, if the samevoltage is applied to each coil, the currents flowing in each coilbecome identical, and the magnitudes of the magnetic fields become alsoidentical.

As a result of this, when the same voltage is applied to each of thecoils in the cross coil, the same magnitude of magnetic field isproduced in each coil, and, for example, when the cross coil is appliedin an indicator, the angle of indication of a pointer accuratelycorresponds to the specified measured value and erroneous indicationscan be prevented.

In addition, each of the first and second coils wound on a coil bobbinsurrounding a magnetic rotor can be divided into two parts and wound oneach side of a shaft of an indicating pointer. The configuration can besuch that the second coil is wound on the outside of the windings ofhalf of the first coil, and the remaining half of the first coil iswound on the outside of the second coil.

If this is done, since the second coil is wound on the outside of thewindings of half of the first coil, and the remaining half of the firstcoil is wound on the outside of the second coil, the direction ofwinding only changes twice in the winding process, thus leading to thesimplification of the manufacturing process of the cross coil.

Since the construction is such that half of the first coil, the secondcoil, and the remaining half of the first coil are wound on thecircumference of the coil bobbin from the inside, in sequence, theundesirable effects on the component of the magnetic field caused fromdifferent distances from the magnetic rotor are cancelled out, therebyaccurate indication characteristics being obtained.

The windings of the coil which are wound onto the magnetic rotor can beformed from a plurality of coil bodies which have both a narrow sectionand a wide section, and form windings of a cross coil with assemblingthese coil bodies by incorporating the wide sections of the coil bodiesto the narrow section of the coil bodies which is adjoined.

By doing this, since the narrow section of the coil body is fitted tothe wide section of the adjacent coil body, a cross coil can be easilyformed from a plurality of coil bodies.

In this cross coil, since the narrow section of each coil body ispositioned symmetrically to the magnetic rotor, the spacing from themagnetic rotor to each coil body is uniform and the magnitude and shapeof each coil body is the same. Further, the balance of the resistancesand the magnetic fields of the coils is also good. Accordingly, errorsin measurement become small.

In addition, the coil bobbin in a conventional coil becomes unnecessary,allowing the size to be reduced by that amount.

These and other objects, features, and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of a conventional crosscoil indicator.

FIG. 2 is a plan view of a conventional cross coil.

FIG. 3 is a phase diagram showing the characteristics of a magneticfield component to be produced in a cross coil.

FIG. 4 is a sectional view showing a conventional cross coil.

FIG. 5 is a phase diagram showing the characteristics of a magneticfield component produced by the cross coil of FIG. 4.

FIG. 6 is an explanatory drawing showing the winding conditions of across coil of a first embodiment of the present invention.

FIG. 7 is an enlarged drawing of the main part of FIG. 6.

FIG. 8 is a plan view of a cross coil of a second embodiment of thepresent invention.

FIG. 9 is a perspective view of a cross coil of a third embodiment ofthe present invention.

FIG. 10 is a sectional view of an indicator in which the cross coil ofthe third embodiment of the present invention is installed.

FIG. 11 is a plan view of the main part of the instrument of FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings, preferred embodiments will be describedin conjunction with the drawings.

FIG. 6 shows the first embodiment of the present invention. In thedrawing, first and second coil windings L₁ and L₂ comprise a pluralityof turns of a wire, respectively. The individual turns of the winding ofa first coil L₁ and a second coil L₂ of a cross coil L are wound one ata time, alternating from one coil to the other. Specifically, one turnof the first coil L₁ is wound, followed by one turn of the second coilL₂, which is wound on top of the first turn. This is then followed byone turn of the first coil L₁, which is wound on top of the second turn.This winding operation is repeated the same number of times for eachcoil so that each coil has the same number of windings. At the pointwhere the two coils L₁ and L₂ cross in this manner, the individualwindings lie, alternately, one on top of the other, as shown in FIG. 7.Each of the two coils includes at least three turns, as shown in FIGS. 6and 7. Accordingly, the total length of the first coil L₁ issubstantially the same as the total length of the second coil L₂.Because the respective resistances are also identical, when the samevoltage is applied to each coil, the magnitudes of the magnetic fieldsφ₁ and φ₂ of the coils L₁ and L₂ become also the same.

In the case where the cross coil of the present invention as describedabove is utilized in a cross coil type indicator, it is possible to makethe currents I_(o) equal and the magnitudes of the magnetic fields φ₁and φ₂ equal as in Equations (1) and (2) so that the magnetic fieldcomponent φ has circular characteristics corresponding to the angle θ,as shown in FIG. 3. Accordingly, if the angle θ is changed in accordancewith a specified measured value, the direction of the magnetic fieldcomponent φ accurately corresponds to the specified measured value. Itis therefore possible to accurately indicate the specified measuredvalue based on the angle θ, using a magnetic rotor M and an indicatingpointer A.

FIG. 8 shows a second embodiment of the present invention. The firstcoil L_(a) and the second coil L_(b) of the cross coil L which comprisesa plurality of turns of a wire, respectively, are each divided into twoparts, resulting in the coils L_(a1), L_(a2), L_(b1), L_(b2)(hereinafter referred to as half-wound sections), each of which has thesame number of windings. The first coil L_(a) and the second coil L_(b)are wound at 90° to each other, and each of the coils L_(a), L_(b) iswound so that the bearings 3a provided on the coil bobbin 3 is locatedbetween the half-wound sections L_(a1) and L_(a2) of the first coilL_(a), and between the half wound sections L_(b1), L_(b2).

As can also be understood from FIG. 8, when winding the cross coil L,first one side of the half-wound section L_(a1) of the first coil L_(a)is wound onto the coil bobbin 3, the winding direction is shifted 90°,then one side of the half-wound section L_(b1) of the second coil L_(b)is wound thereon, by shifting the winding direction at 90° with respectto the half-wound section L_(a1) of the first coil L_(a). In thiscondition, the half-wound section L_(b2), which is connected to thehalf-wound section L_(b1), is also wound on the opposite side of thebearing 3a in the same manner as the half-wound section L_(b1) of thesecond coil L_(b). Then, when the winding of the half-wound sectionsL_(b1) and L_(b2) of the second coil L_(b) is completed, the windingdirection is again shifted 90°, and the remaining half-wound sectionL_(a1) of the first coil L_(a) is wound opposite the half-wound sectionL.sub. a1 such that the bearing 3a is inserted between the half-woundsections L_(a1) and L_(a2).

By means of the cross coil L wound in this manner, the half-woundsections L_(b1) and L_(b2) of the second coil L_(b) are arranged at thesame distance respectively from the magnetic rotor 2. On the other handin the first coil L_(a), the half-wound section L_(a1) is closer to themagnetic rotor 2 than the second coil L_(b), and the half-wound sectionL_(a2) is further away from the second coil L_(b).

Accordingly, the magnetic field component of the half-wound sectionsL_(a1) and L_(a2), specifically, the magnetic field of the first coilL_(a), and the magnetic field component of the half-wound sectionsL_(a1), L_(a2), specifically, the magnetic field of the second coilL_(b), become substantially equal. The change in the azimuth angle(indicated value) of the magnetic field components of the first coilL_(a) and the second coil L_(b), with respect to the phase angle θ ofthe input current explained in FIG. 3, becomes linear, so that itbecomes possible to accurately indicate the measured value.

In addition, in the cross coil L as previously described, the secondcoil L_(b) (half wound sections L_(b1) and L_(b2)) is wound on theoutside of the windings of the half wound section L_(a1) of the firstcoil L_(a), and the remaining half wound section L_(a2) of the firstcoil L_(a) is wound on the outside of the second coil L_(b). Thereforeit is only necessary to change direction twice during the windingprocess, thus leading to the simplification of the winding process.Namely, this is a very simple method compared with the conventionalwinding process in which each layer is wound alternately since it issufficient to change the winding direction twice in the winding process.

In the foregoing embodiment of the present invention, the number ofwindings on the half-wound sections L_(a1), L_(a2), L_(b1) and L_(b2) ofwhich the cross coil L is constructed is the same. However, because thenumber of windings on a cross coil is generally large, even when thereis a slight difference in the number of windings on each half-woundsection, it is possible to obtain the same effect as described above, ifthe first coil is almost divided into two half-wound sections, and ifthe winding is alternately performed in the order of one of thehalf-wound sections of the first coil, the second coil and the remaininghalf of the first coil.

In a cross coil type indicator incorporating the cross coil of thepresent invention as explained above, the first and second coils, wouldsuch that the windings cross each other and enclose the magnetic rotor,are respectively divided into two halves and wound on both sides of theindicating pointer shaft. The two half-wound sections of the second coilis wound on the outside of the windings of half of the first coil, andthe remaining half of the first coil is wound on the outside of thesecond coil. For this reason, the winding of the cross coil can becompleted by changing the direction of winding twice only. In addition,because the construction is such that one half of the first coil, thesecond coil, and the remaining half of the first coil are wound on thecircumference of the magnetic rotor from the inside, in sequence, theeffects on the magnetic field component resulting from the difference indistance from the magnetic rotor are cancelled out.

Accordingly, this winding process also makes it possible to easilyobtain a cross coil type instrument with accurate indicationcharacteristics.

FIG. 9 shows a third embodiment of the present invention. As shown inthe drawing, a cross coil 31 according to the present inventioncomprises four coil bodies 34 to be assembled into a surround such as agrid-like shape. Each of the coil bodies 34 which compriese a pluralityof turns of a wire is provided with a narrow section 32 and a widesection 33 into which a narrow section 22 of the adjacent coil body 34is incorporated. Specifically, the configuration of the cross coil ofthis embodiment is such that the narrow sections 32 of four coil bodies34 are fitted into the inside walls of the wide sections 33 of therespective adjacent coil body 34, respectively.

In this case, each of the coil bodies 34 is fabricated in the desiredshape after being wound with wires so as to have a hollow space thereinby using a press forming method or the like. This coil body may bemolded by a resin material.

As shown in FIG. 9, in thus assembled coil bodies 34, a magnetic rotor35 is provided.

FIG. 10 is a sectional view showing a movement for an indicator usingthe cross coil 31 of the third embodiment. FIG. 11 is a plan view of themain part of the indicator of FIG. 11. In the cross coil 31, the outerwall of the wide section 33 of the coil body 34 is interposedlysupported between an upper frame 36 and a lower frame 37 made ofplastic. A rotating shaft 40 of a magnetic rotor 35 is supported in afreely rotatable manner by a pair of bearings 38, 39 with respect to theframes 36, 37. The magnetic rotor 35 is provided in a freely rotatablemanner on the inside of the cross coil 31 thus assembled.

A starting end 41 and a terminating end 42 of the single wire whichforms each coil 34 are connected to one end of a pin-shaped terminal 43which is embedded in the lower frame 37 and the other end of the pinshaped terminal 43 which is soldered to a printed circuit of a controlwiring board 44, respectively.

A tubular magnetic shield plate 45 and a lower plate 46 for an indicatorcasing of the indicator are provided.

Here, when a current proportional to a vehicle speed is supplied intothe coil body 34 from the control wiring board 44 via the terminal 43, amagnetic field component is produced at the cross coil 31 so that themagnetic rotor 35 rotates in that direction. As a result, the speed isdisplayed by an indicating pointer 47 provided on the rotary shaft 40.

In this state, the magnitudes and shapes of the coil bodies 34 are thesame, respectively. Also, the space L between the narrow section 32 ofthe coil body 34 and the magnetic rotor 35 is the same for all the coilbodies 34. Therefore, there is good balance between the resistance andthe magnetic field of the coil, so the accuracy of measurement isimproved several stages in comparison with a conventional cross coil inthe same manner as the embodiments as described above.

Further, according to this embodiment, each coil body 34 is formed asone part comprising windings, it is not necessary to wind a coil windingat the manufacturing process thereof. Therefore, the manufacturingprocess of a cross coil becomes remarkably easy.

It must be understood that the invention is in no way limited to theabove embodiments and that many changes may be brought therein withoutdeparting from the scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A cross coil in a cross coil indicator of the type having a magnetic rotor rotatably provided within a coil bobbin in which the rotor is rotated by the magnetic field component generated in the cross coil, which comprises:means for generating a first magnetic field when an electrical current flows therethrough, comprising a first coil winding composed of at least one turn of an electrical conductor and disposed on the coil bobbin; means for generating a second magnetic field when an electrical current flows therethrough, comprising a second coil winding composed of turns of an electrical conductor equal to the number of turns of the first coil winding and disposed on the coil bobbin, the second coil winding being wound around the coil bobbin so as to cross the first coil winding such that said first coil winding and said second coil winding are crossed relative to each other, and wherein the magnetic rotor is rotated by the magnetic field component of the first and second magnetic fields; and means for equalizing the magnitude of each of the first and second magnetic fields generated when the identical voltage is applied to each of the coil windings, wherein each respective coil winding equals the other winding in length and each coil winding has the same resistance value.
 2. The cross coil as claimed in claim 1, wherein the first and second coil windings comprises a plurality of turns of a wire, respectively, and the number of the turns for each winding being the same, and the equalizing means comprises the arrangement of the turns of the windings in which the individual turns are alternately wound on top of the turns for the other winding.
 3. The cross coil as claimed in claim 2, wherein the cross coil further comprises a coil bobbin in which the magnetic rotor which is rotated by the magnetic fields component of the first and second magnetic fields is to be disposed, and the first and second coil windings are wound around the coil bobbin.
 4. The cross coil as claimed in claim 1, wherein each of the first and second coil windings is divided into two winding sections, and the equalizing means comprises the arrangement of the winding sections of the first and second coil winding in which two winding sections of the second coil winding are wound onto one winding section of the first coil winding and the other winding section of the first coil winding is wound onto the two winding sections of the second coil winding.
 5. The cross coil as claimed in claim 4, wherein the two coil winding sections of the respective first and second coil windings are arranged substantially parallel to each other.
 6. The cross coil as claimed in claim 5, wherein each of the first and second coil windings comprises at least one coil body having a flattened ring-like shape with narrow and wide sections, and the equalizing means comprises the arrangement of the coil bodies of the first and second coil windings in which the narrow sections of the coil bodies are fitted into the wide sections of the adjacent coil bodies.
 7. The cross coil as claimed in claim 1, wherein each of the first and second coil winding is divided into two coil bodies each having a flattened ring-like shape with narrow and wide sections, and the equalizing means comprises the arrangement of the coil bodies of the first and second coil windings in which the narrow sections of the coil bodies are fitted into the wide sections of the adjacent coil bodies.
 8. The cross coil as claimed in claim 7, wherein each of the coil bodies has the same size and shape, and the four coil bodies are assembled so as to form a square surround in which the magnetic rotor which is rotated by the magnetic field components of the first and second magnetic fields in which the magnetic rotor is to be disposed.
 9. The cross coil as claimed in claim 8, wherein each of the coil bodies is formed of a plurality of turns of a wire pressed into the flattened ring-like shape and having a certain hardness.
 10. The cross coil as claimed in claim 9, wherein the assembled square surround constitutes a coil bobbin in which the magnetic rotor is disposed.
 11. The cross coil as claimed in claim 6, wherein each of the coil bodies has the same size and shape, and the four coil bodies are assembled so as to form a square surround in which the magnetic rotor which is rotated by the magnetic field components of the first and second magnetic fields in which the magnetic rotor is to be disposed.
 12. The cross coil as claimed in claim 11, wherein each of the coil bodies is formed of a plurality of turns of a wire pressed into the flattened ring-like shape and having a certain hardness.
 13. The cross coil as claimed in claim 12, wherein the assembled square surround constitutes a coil bobbin in which the magnetic rotor is disposed.
 14. A cross coil type indicator, comprising:a coil bobbin; a magnetic rotor rotatably provided within the coil bobbin, to which a pointer axis is cooperatively connected; and a cross coil arranged around the coil bobbin in such a manner the rotor is rotated by a magnetic field component generated in the cross coil, wherein the cross coil comprises:a first coil winding for generating a first magnetic field which an electrical current flows therethrough, the first coil winding comprising a plurality of at least three turns of a wire wound around the coil bobbin; and a second coil winding for generating a second magnetic field when an alectrical current flows therethrough, the second coil winding comprising a plurality of at least three turns of a wire which is formed from the same type wire as that of the first coil winding, the turn number of the second coil winding being the same as that of the turns of the first coil winding, wherein the respective turn of the plural turns of one coil winding is alternately wound on the respective turn of the plural turns of the other coil winding with each other such that the wire length of each winding becomes equal and the wire of each winding has the same resistance value. 